Dismissed as a laboratory curiosity in the 1970s, homogeneous charge-compression ignition (HCCI) has now emerged as a more feasible alternative to alternative fuels--and it's almost ready to roll out en masse. When used in conjunction with other advanced engine technologies, this combustion process can help deliver a whopping 25- to 30 -percent better fuel economy than today's spark- or compression-ignited internal combustion engines (ICE). HCCI does all this with near-zero emissions, just like a hybrid--and it won't have any impact on your driving habits or come at a premium price.

General Motors is to a large extent leading the big new charge to re-engineer the engine, and they recently offered Popular Mechanics an exclusive tour in the depths of their Research and Development Center in Warren, Mich. That's where HCCI's Paul Najt runs the Powertrain Systems Research Lab--and has some serious gear for making this revolutionary compression technology, well, try to save the world. [Check out inside-the-lab video from PopMech TV here; story continues below ...]

So what makes the HCCI process different from spark or compression ignition? It delivers a more complete, efficient burn at temperatures too low for the formation of harmful nitrous oxides. As a result, the job of cleaning the exhaust becomes much easier, resulting in fewer greenhouse gases being expelled into the atmosphere. It also requires a much leaner air/fuel mixture (less fuel, more air) for detonation than in a standard four-stroke engine--hence the 25- to 30- percent bump in fuel economy. Plus, burning gasoline at a lower temperature means that considerably less energy is lost through the exhaust pipe, or transferred as waste heat into the engine's cooling system.

Originally known as active thermo-atmosphere combustion, HCCI was first discovered in 1979 by engineers at the Nippon Clean Engine Research Institute in Japan trying to perfect a cleaner, more efficient two-stroke engine. But at the time HCCI couldn't be controlled well enough to work in a four-stroke engine. Advances in microprocessors, sensors and control systems have somewhat rectified that problem, sending nearly every top-tier carmaker (notably GM with the process explained above, Honda with activated radical combustion and Mercedes-Benz with its DiesOtto program) as well as a consortium of U.S. universities and government labs (recently contracted by the Department of Energy) into overdrive as they scramble to perfect an engine that employs HCCI.

"Remember, hybrids and plug-in electric vehicles use an internal combustion engine as their primary mover," explains Amory Lovins, founder of the super--efficient Rocky Mountain Institute think tank and winner of PM's 2007 Breakthrough Leadership Award. "So unless we go to pure battery power or fuel cells sooner than anticipated, don't discount the role of the ICE."

That's why researchers from Najt at GM to those in startups across the globe are working on advanced engine technologies to clean up the internal combustion process and make it more efficient. Whether HCCI is the real thing or just a placebo, it's suddenly become the most expedient bridge to a fuel-efficient driving solution that we've got.